Segmented Routing for Speed-Performance and Routability in Field-Programmable Gate Arrays

This paper addresses several issues involved for routing in Field-Programmable Gate Arrays (FPGAs) that have both horizontal and vertical routing channels, with wire segments of various lengths. Routing is studied by using CAD routing tools to map a set of benchmark circuits into FPGAs, and measuring the effects that various parameters of the CAD tools have on the implementation of the circuits. A two-stage routing strategy of global followed by detailed routing is used, and the effects of both of these CAD stages are discussed, with emphasis on detailed routing. We present a new detailed routing algorithm designed specifically for the types of routing structures found in the most recent generation of FPGAs, and show that the new algorithm achieves significantly better results than previously published FPGA routers with respect to the speed-performance of implemented circuits. The experiments presented in this paper address both of the key metrics for FPGA routing tools, namely the effective utilization of available interconnect resources in an FPGA, and the speed-performance of implemented circuits. The major contributions of this research include the following: 1) we illustrate the effect of a global router on both area-utilization and speed-performance of implemented circuits, 2) experiments quantify the impact of the detailed router cost functions on area-utilization and speed-performance, 3) we show the effect on circuit implementation of dividing multi-point nets in a circuit being routed into point-to-point connections, and 4) the paper illustrates that CAD routing tools should account for both routability and speed-performance at the same time, not just focus on one goal.